libgnt/libgnt

Define G_LOG_DOMAIN during our build so our logs will show where the come from.

Testing Done:
Built and ran a few of the manual tests.

Reviewed at https://reviews.imfreedom.org/r/191/
option('doc', type : 'boolean', value : true, yield : true,
description : 'build documentation with gtk-doc')
option('introspection', type : 'boolean', value : true, yield : true,
description : 'build introspection data')